(1) Field of the Invention
The present invention relates to an apparatus and a method for resource request arbitration, and more specifically, it relates to a technique to control service qualities for each of a plurality of resource requesting devices that are subject to arbitration.
(2) Description of the Related Art
An information processor that is structured so as to enable a plurality of resource requesting devices to access to a shared resource such as a bus and a unified memory has been known. Each resource requesting device in the information processor issues a resource request as needed in order to access the shared resource, without concerning the status of the other resource requesting devices. The information processor prevents an access conflict to the shared resource between more than one resource requesting device by a process called arbitration for acknowledging one of the resource requesting devices when more than one resource request is issued almost at the same time.
The arbitration is easily realized by setting a static priority for each of the plurality of resource requesting devices, and acknowledging a resource request that is issued by a resource requesting device with the highest priority. A technique called a round-robin arbitration is also known, which ensures the fairness among the resource requesting devices by rotating the priority order.
Further, in a case of a resource requesting device that processes data such as moving images, which requires a high degree of real-time processing, an effective control of the service qualities, indicated by such as the data transfer rate and the maximum waiting time, have been demanded, in addition to the fairness.
An arbitrating device disclosed in Japanese Laid-Open Patent Application No. H10-289203 is made in an attempt to respond to such demands. The arbitrating device of H10-289203 controls the service qualities in a manner that the arbitrating device compares an actual amount of transfer data and an amount of data to-be-transferred for each of the resource requesting devices that are subject to arbitration, and when the data transfer of one of the resource requesting devices is smaller than the amount of data to-be-transferred, and the data transfer of another of the resource requesting devices is larger than the amount of data to-be-transferred, the arbitrating device acknowledges the resource request issued by the former device.
By using the technique disclosed in H10-289203, the arbitrating device compares and judges a status of each resource requesting device, and re-arranges the priority order dynamically in order to control the service qualities. Therefore, a problem has been noted that, when the number of resource requesting devices that are subject to arbitration increases, the processing according to the arbitration technique disclosed in H10-289203 becomes drastically complicated as the number of combination of the devices issuing requests increases.